1. Field of the Invention
The present invention relates to a diffuse reflection plate to be used in a reflection-type display device and a manufacturing method thereof as well as to a reflection-type display device using a diffuse reflection plate.
2. Description of the Related Art
Having a flat panel shape, display devices using a liquid crystal or the like as an electro-optical layer have features that they are light, thin, and of low power consumption. For this reason, such display devices are being developed enthusiastically as displays of portable equipment, for example. Electro-optical materials such as a liquid crystal are not of a spontaneous light emission type and produce an image by selectively transmitting and interrupting external light. Passive display devices of this type are classified into the transmission type and the reflection type by the illumination method.
In a transmission-type display device, a panel in which an electro-optical layer such as a liquid crystal layer is held between two transparent substrates is manufactured and a light source (backlight) for illumination is disposed on the back side of the panel. An image is observed from the front side of the panel. In the case of the transmission type, the backlight is indispensable and a cold-cathode tube or the like is used as a light source. Since the backlight consumes most of the energy that is consumed by the entire display, transmission-type devices are not suitable for a display of portable equipment. On the other hand, in the case of the reflection type, a reflection plate is disposed on the back side of a panel and external light such as natural light is input from the front side. An image is observed from the front side as in the case of the transmission type by utilizing reflection light of the input external light. Not using a light source for back illumination unlike transmission-type devices, reflection-type devices are of relatively low power consumption and hence suitable for a display of portable equipment.
In reflection-type display devices, because display is performed by utilizing incident light coming from the environment, it is necessary to increase the luminance by effectively utilizing the incident light. Further, to realize white display (what is called paper white), basically it is necessary to diffuse-reflect incident light within the panel. To this end, conventional reflection-type display devices incorporate a diffuse reflection layer within the panel. It is intended that the diffuse reflection layer have a characteristic that is close to perfect diffusion and assume an appearance that as close to paper white as possible.
However, display devices have a mode in which an image is produced by utilizing a linearly polarized component of incident light. In this mode, there may occur a case that when a diffuse reflection plate having a perfect diffusion characteristic is used, sufficiently high contrast cannot be obtained because the polarization state of incident light is disordered.
Where a reflection-type display device is illuminated in a room by using an auxiliary light source such as a desk lamp, causing incident light from the light source to be reflected efficiently toward a viewer is effective for increase in luminance. However, conventional diffuse reflection layers having perfect diffusion do not have what is called directivity and hence cannot make effective use of incident light when combined with an auxiliary light source or the like.